On the basis of work conducted in our laboratory and in other labs, we have proposed that male copulatory behavior of the rat is controlled, in part, by a neural system which includes the medial preoptic area (mPOA), the medical forebrain bundle (MFB) of the hypothalamus and midbrain extensions of the MFB. The overall objective of this project is to subject this hypothesis to rigorous testing at three levels of analysis: 1) anatomical, 2) behavioral and 3) neurochemical. We plan to surgically interrupt this proposed system at several levels along it's telencephalic - hypothalamic - midbrain extension in an attempt to further identify the critical connections. Preparations which result in sexual deficits will be compared and contrasted in terms of the nature of the behavioral impairment produced. A series of behavioral tests designed to identify subtle changes in the male's responsiveness to sexual stimuli will be developed for this purpose. Finally, since this proposed system includes major projections from ascending monoamine pathways recently identifies by histochemical fluorescence procedures, neurochemical analysis of behaviorally disruptive lesions will be included.